High-yield dual-buffered bacterial growth medium

Abstract

A novel growth medium called "H15" is disclosed that supports much higher E. coli cell densities and, concomitantly, a much higher yield of plasmid than previously reported for small-scale applications. The high-yield growth medium contains two buffers with different pKa values and an additional nucleotide source. On a unit volume basis, E. coli cultures grown in this medium consistently produce 5-10 times, and sometimes up to 30 times, more recombinant plasmid than in conventional rich media, paralleling the increase in cell density. This phenomenon is independent of E. coli host strain, DNA insert size and plasmid copy number. H15 medium is economical and high yields can be achieved using standard research laboratory equipment.

We claim:  
     
       1. A bacterial growth medium comprising: 
       (a) an effective amount of a first buffer having a pKa between about 6.6 and about 7.5;  
       (b) an effective amount of a second buffer having a pKa between about 7.5 and about 8.0;  
       (c) an effective amount of free RNA;  
       (d) an effective amount of an RNase enzyme; and  
       (e) an effective amount of bacterial nutrients.  
     
     
       2. A bacterial growth medium as recited in  claim 1 , wherein the components of said medium are in aqueous solution. 
     
     
       3. A bacterial growth medium as recited in  claim 2 , wherein the initial pH of said medium is about 7.6 to about 7.7. 
     
     
       4. A bacterial growth medium as recited in  claim 1 , wherein said medium comprises: 
       (a) between about 5 and about 20 parts RNA by weight;  
       (b) between about 20 and about 80 parts yeast extract by weight;  
       (c) between about 5 and about 20 parts casamino acids by weight;  
       (d) between about 15 and about 25 parts glucose by weight;  
       (e) between about 46 parts and about 59 parts 3-(N-morpholino)-propanesulfonic acid;  
       (f) between about 27 parts and about 40 parts tris-(hydroxymethyl)aminomethane; and  
       (g) between about 0.0015 and about 0.015 parts RNase A by weight.  
     
     
       5. A bacterial growth medium as recited in  claim 4 , wherein said medium comprises about 10 parts RNA by weight. 
     
     
       6. A bacterial growth medium as recited in  claim 4 , wherein said medium comprises about 50 parts yeast extract by weight. 
     
     
       7. A bacterial growth medium as recited in  claim 4 , wherein said medium comprises about 10 parts casamino acids by weight. 
     
     
       8. A bacterial growth medium as recited in  claim 4 , wherein said medium comprises about 20 parts glucose by weight. 
     
     
       9. A bacterial growth medium as recited in  claim 4 , wherein said medium comprises about 52.3 parts 3-(N-morpholino)-propanesulfonic acid by weight. 
     
     
       10. A bacterial growth medium as recited in  claim 4 , wherein said medium comprises about 42.95 parts tris-(hydroxymethyl)aminomethane by weight. 
     
     
       11. A bacterial growth medium as recited in  claim 4 , wherein said medium comprises about 0.01 parts RNase A by weight. 
     
     
       12. A bacterial growth medium as recited in  claim 4 , additionally comprising water in an amount sufficient to bring the total volume to 1000 parts. 
     
     
       13. A bacterial growth medium as recited in  claim 12 , wherein the initial pH of said medium is about 7.6 to about 7.7. 
     
     
       14. A method comprising growing bacteria in a bacterial growth medium as recited in  claim 12 , wherein during both the exponential and the secondary phases of bacterial growth the pH is always within the range between about 6.5 and about 8.0. 
     
     
       15. A method comprising growing bacteria in a bacterial growth medium as recited in  claim 12 , wherein the bacteria acidifies the medium, the first buffer preventing the pH dropping below about 6.5; then the bacteria excretes basic metabolites, the second buffer preventing the pH rising above about 8.0; whereby the pH is maintained between about 6.5 and 8.0; thereby enhancing growth of the bacteria. 
     
     
       16. A method as recited in  claim 14 , additionally comprising aerating the medium during bacterial growth. 
     
     
       17. A method as recited in  claim 14 , wherein the bacteria comprise at least one exogenous plasmid, additionally comprising the step of extracting plasmid DNA from the bacteria following the secondary phase of bacterial growth. 
     
     
       18. A method as recited in  claim 14 , wherein the bacteria comprise at least one exogenous gene encoding a recombinant protein, additionally comprising the step of extracting recombinant protein from the bacteria or the medium following the secondary phase of bacterial growth. 
     
     
       19. A bacterial growth medium comprising: 
       (a) an effective amount of a first buffer having a pKa between about 6.6 and about 7.5;  
       (b) an effective amount of a second buffer having a pKa between about 7.5 and about 8.0;  
       (c) an effective amount of RNA; and  
       (d) an effective amount of bacterial nutrients.  
     
     
       20. A bacterial growth medium as recited in  claim 19 , wherein the components of said medium are in aqueous solution. 
     
     
       21. A bacterial growth medium as recited in  claim 20 , wherein the initial pH of said medium is about 7.6 to about 7.7. 
     
     
       22. A bacterial growth medium as recited in  claim 19 , wherein said medium comprises: 
       (a) between about 20 and about 80 parts yeast extract by weight;  
       (b) between about 5 and about 20 parts casamino acids by weight;  
       (c) between about 15 and about 25 parts glucose by weight;  
       (d) between about 46 parts and about 59 parts 3-(N-morpholino)-propanesulfonic acid;  
       (e) between about 27 parts and about 40 parts tris-(hydroxymethyl)aminomethane; and  
       (f) between about 5 and about 20 parts RNA by weight.  
     
     
       23. A bacterial growth medium as recited in  claim 22 , additionally comprising water in an amount sufficient to bring the total volume to 1000 parts. 
     
     
       24. A bacterial growth medium as recited in  claim 23 , wherein the initial pH of said medium is about 7.6 to about 7.7. 
     
     
       25. A method comprising growing bacteria in a bacterial growth medium as recited in  claim 23 , wherein during both the exponential and the secondary phases of bacterial growth the pH is always within the range between about 6.6 and about 8.0. 
     
     
       26. A method comprising growing bacteria in a bacterial growth medium as recited in  claim 23 , wherein the bacteria acidifies the medium, the first buffer preventing the pH dropping below about 6.5; then the bacteria excretes basic metabolites, the second buffer preventing the pH rising above about 8.0; whereby the pH is maintained between about 6.5 and 8.0; thereby enhancing growth of the bacteria. 
     
     
       27. A method as recited in  claim 25 , additionally comprising aerating the medium during bacterial growth. 
     
     
       28. A method as recited in  claim 25 , wherein the bacteria comprise at least one exogenous plasmid, additionally comprising the step of extracting plasmid DNA from the bacteria following the secondary phase of bacterial growth. 
     
     
       29. A method as recited in  claim 25 , wherein the bacteria comprise at least one exogenous gene encoding a recombinant protein, additionally comprising the step of extracting recombinant protein from the bacteria or the medium following the secondary phase of bacterial growth.